1. Field of the Invention
The invention pertains to the production of 1,1-difluoroethane, or more particularly to the production of 1,1-difluoroethane by the reaction of 1,2-dichloroethane with anhydrous hydrogen fluoride in a liquid phase and in the presence of a Lewis acid.
2. Description of the Prior Art
Hydrofluorocarbons or HFC's are of interest due to their potential to replace ozone depleting chlorofluorocarbons or CFC's in a variety of applications, including refrigerants, aerosol propellants, foam blowing agents and solvents. 1,1-difluoroethane, HFC-152a, has been identified as a useful aerosol propellant and a component in refrigerant blends and has no known ozone depletion potential. It is not classified as a volatile organic compound and has very low global warming potential. Therefore, HFC-152a is an ideal candidate to replace chlorofluorocarbon propellants in such consumer products as antiperspirants and hairsprays.
There are known methods for producing 1,1-difluoroethane. Japanese Kokai JP6-228021 fluorinates 1,1-dichloroethane. Canadian patent 832,502 reacts a mixture of 1,2-dichloroethane and vinyl chloride with hydrogen fluoride in a vapor phase in the presence of a chrome oxide catalyst with subsequent separation of produced vinyl fluoride and 1,1-difluoroethane. U.S. Pat. No. 2,452,975 fluorinates a polychlorinated ethane to a polyfluorinated ethane, however, at least two chlorine atoms must be attached to the same carbon atom. U.S. Pat. No. 3,978,145 fluorinates halogenated aliphatic compounds with hydrogen fluoride, however this is done in a vapor phase using a hexagonal chromium(III) oxide hydroxide. Chinese patent application 92100388.9 teaches the fluorination of chloroethylene. U.S. Pat. No. 3,190,930 prepares 1,1-difluoroethane by reacting acetylene and hydrogen fluoride. Liquid phase fluorination of 1,2-dichloroethane to give HFC-152a is not known in the art. Although the above chloroethane feeds for HFC-152a processes are commercially available, 1,1-dichloroethane is more expensive than 1,2-dichloroethane. The gas phase fluorination of 1,2-dichloroethane has several disadvantages, namely, a higher reaction temperature, formation of large quantity of vinyl chloride intermediate and poor selectivity of 1,1-difluoroethane. Vinyl chloride is carcinogenic and difficult to separate for recycling. Its propensity to polymerize in the presence of hydrogen fluoride will often lead to varying quantities of coke which leads to reduced catalyst life time. At lower temperatures(&lt;200.degree.0 C.), the reaction does not proceed sufficiently to give 1,1-difluoroethane and at higher reaction temperatures(&gt;400.degree. C.), degradation of catalyst and a mixture of vinyl chloride, vinyl fluoride and 1,1-difluoroethane are formed. Separation of this mixture to obtain pure 1,1-difluoroethane by distillation is tedious and expensive. It would therefore be advantageous to provide a process for the production of 1,1-difluoroethane by the reaction of 1,2-dichloroethane with anhydrous hydrogen fluoride in a liquid phase.